Change the way Perl modules are installed, update the default Perl to 5.18.
Before, we had:
site_perl : lib/perl5/site_perl/5.18
site_perl/perl_arch : lib/perl5/site_perl/5.18/mach
perl_man3 : lib/perl5/5.18/man/man3
Now we have:
site_perl : lib/perl5/site_perl
site_arch : lib/perl5/site_perl/mach/5.18
perl_man3 : lib/perl5/site_perl/man/man3
Modules without any .so will be installed at the same place regardless of the

Fix unixODBC vs libiodbc conflicts
Always rely on unixODBC each time a port is looking for libodbc.so
Remove odbc compat from libiodbc
This allows to install both kde and gnome at the same time
While here:
- Convert libiodbc to USES=libtool
- Convert a bunch of libiodbc dependencies to USES=libtool
- Chase libiodbc.so shlib change
- Stagify some ports
- Convert some ports to USES=pgsql
Discussed with: rakuco (kde)
With hat: portmgr

Conditionalise dependencies on databases/p5-DBI: for perl
5.005_03 use databases/p5-DBI-137 as newer versions do not
support the old perl.
Note that for some port, I merely removed the explicit
dependency as they already have implicit dependencies
via other ports.
Approved by: portmgr (marcus)